Volunteers undergo tolerance training in preparation for sit-in demonstrations in Petersburg, Virginia, in May 1960. Here, Leroy Hill (left) and another man blow smoke into the face of an unidentified volunteer.

A woman, unable to find a vacant seat at an F.W. Woolworth's lunch counter, chastises demonstrators participating in a sit-in protest on April 2, 1960.

Getty Images

Left: Members of the American Nazi Party stage a counterdemonstration during a sit-in at a drugstore lunch counter in Arlington, Virginia. Right: Robert Fehsenfeld, owner of the Dizzyland Restaurant, smashes an egg in a white demonstrator's face during a sit-in at his restaurant on July 8, 1963. Fehsenfeld also kicked several demonstrators and threw a glass of water in one's face.

Bettmann / Bettmann Archive

Professor John R. Salter, Joan Trumpauer, and Anne Moody remain at a sit-in at a lunch counter in Jackson, Mississippi, even after Salter was sprayed with condiments and beaten on the back and head by spectators in the crowd.

AP Photo

Left: Dion Diamond, a student at Howard University, is confronted by white youths during a sit-in demonstration at an Arlington, Virginia, drugstore on June 9, 1960. Right: Charles Barnes Jr. (white shirt), throws a sit-in demonstrator out of the restaurant owned by his father in Annapolis, Maryland, on March 3, 1964. Police arrested 16 of the protesters when they wouldn't move from the sidewalk.

People chain themselves in front of the New York City Hall on Aug. 23, 1963, during a protest against segregation.

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As they are filmed by news cameras, police officers carry sit-in protesters down the steps of the US Capitol Building on March 15, 1965.

AP Photo

Left: Rev. Avery Alexander is dragged feetfirst by police after he led a sit-in demonstration at City Hall in New Orleans on Oct. 31, 1963. Right: Dr. Martin Luther King Jr. stands in a cell at the St. John's County Jail in St. Augustine, Florida, after he was arrested for integration attempts at a local motel restaurant.

Anonymous / AP

An unidentified man is dragged from the street in Nashville on April 29, 1964, as civil rights demonstrators sat down in front of a segregated restaurant. Police arrested 50 or more during the third day of demonstrations.

AP

Army National Guard soldiers, one armed with a tear gas gun, prepare to stop a civil rights demonstration on May 13, 1964.

AP Photo

Left: Muriel Lawton and her granddaughter, Katherine, were among 500 demonstrators who staged a sit-in at a construction site in Brooklyn on July 22, 1963. Some 200 demonstrators were arrested. Right: State police surround an unidentified demonstrator after they battered him to the ground with their clubs on Aug. 31, 1963, in Folcroft, Pennsylvania.

Children wait while their parents hold a sit-in in Aurora, Colorado, on Sept. 30, 1962. From left: Kim Schweizer, 3; Frederick Hawkins, 3; and Karin Schweizer. Frederick's parents, Mr. and Mrs. Lee Hawkins, say that they were refused a home because of their race.

AP Photo

Under umbrellas for shade, Southern University students kneel on the school's baseball diamond to pray on March 31, 1960, for 18 fellow students who were expelled for participating in a sit-in. Hundreds attended the meeting, which was held to give instructions for orderly mass withdrawal from school in protest of expulsion of fellow students.

Fred Waters / AP

A crowd of demonstrators take part in a sit-in the middle of Locust Street during rush hour in St. Louis to protest alleged resegregation in the city's schools on June 21, 1963. The peaceful sit-in was staged in front of the school board building. Police arrested two white men who they said swore at the demonstrators.

Anonymous / AP

Martin Luther King Jr. and civil rights marchers cross the Edmund Pettus Bridge in Selma, Alabama, heading for the state capitol building in Montgomery on March 21, 1965.

Bettmann / Bettmann Archive

Demonstrators gather in front of the Washington Monument awaiting the start of the March on Washington ceremony and to hear what would be known as Martin Luther King Jr.'s "I Have a Dream" speech on Aug. 28, 1963.

Gabriel H. Sanchez is the photo essay editor for BuzzFeed News and is based in New York City.